What is the ruling on depositing money in an Islamic bank and taking interest from it? Is this permissible as an exception for special cases, such as a disabled daughter or a widow over seventy years old, who do not have a fixed income other than the returns from this money?

It is permissible to deal with Islamic banks whose transactions are sharia (definition)-compliant, and for the investor to engage in Mudarabah (definition) (profit-sharing) with them, and their profits are lawful. As for banks that are not sharia-compliant, it is not permissible to deposit money with them and take usurious interest, except in cases of extreme necessity.